有没有更有效的乘法字节数组的方法？

I developed a Golang package BESON for doing operation of big number.

The Multiply operation code:

func Multiply(a []byte, b []byte) {
    ans := make([]byte, len(a) + len(b))
    bits := nbits(b)

    var i uint
    for i = bits - 1; int(i) >= 0; i-- {
        byteNum := i >> 3
        bitNum := i & 7

        LeftShift(ans, 1, 0)
        if (b[byteNum] & (1 << bitNum)) > 0 {
            Add(ans, a)
        }
    }
    copy(a, ans)
}

My way is to add every a multiply bits of b. Is there more efficient way to implement Multiply?

Edit

The BESON package represent a big number in byte array. For example, it represent a 128-bit unsigned interger in an byte array of size 16. Therefore, when doing two 128-bit unsigned interger multiplying, it's actually multiplying two byte array.

Example:

• input: a, b

a = []byte{ 204, 19, 46, 255, 0, 0, 0, 0 }
b = []byte{ 117, 10, 68, 47, 0, 0, 0, 0 }
Multiply(a, b)
fmt.Println(a)

• output: a (The result will write back to a)

[60 4 5 35 76 72 29 47]